This invention relates to hydraulically or pneumatically actuated muscles, that is, devices which convert a fluid pressure into a tensive force. The invention is more specifically directed to an improved arrangement for the elongated elastomeric bladder of the muscle.
Hydraulic and pneumatic muscles can be favorably employed in an elongated flexible probe such as an borescope or endoscope for actuating its articulation or steering section. With the use of fluid muscles, the conventional long steering cables can be eliminated. This use of a fluid muscle in a borescope or endoscope is described in U.S. Pat. No. 4,962,751, filed May 30, 1989, and having a common assignee herewith. Another fluid dynamic muscle in a borescope or endoscope is described in U.S. Pat. No. 4,794,912, granted Jan. 3, 1989.
Fluid dynamic articulation and steering for a borescope or endoscope offers a distinct improvement over the conventional systems of steering cables, permitting much more accurate and precise positioning of the viewing end of the instrument within the cavity to be inspected and permitting much longer articulating borescopes or endoscopes to be built.
The hydraulic, pneumatic, or fluid dynamic muscle is made up of an elongated tubular bladder which is encased in an elongated tubular braid member disposed over it. Terminators are provided at the proximal and distal ends of the muscle to seal the ends of the bladder and to provide a place for mechanical attachment between the ends of the braid member and the mechanical members to which they are to transfer force, e.g. a cable or a muscle sheath. The braid permits the bladder within the muscle to expand laterally, i.e., radially, when fluid pressure is applied to it. As the bladder and braid expand radially, the braid contracts axially and generates an axial tensive force.
On the other hand, tension on the cable tends to stretch the muscle axially, and to squeeze the bladder radially. The amount of elongation depends upon the capacity of the bladder and its residual internal cross section when the muscle is fully elongated.
These muscles are usually employed in pairs, with one of the muscles being used to deflect the borescope steering section in one direction (i.e., to the left) and the other muscle being actuated to deflect the steering section in the other direction (i.e., to the right). To achieve optimal steering, both muscles should have identical performance characteristics. However, the present techniques for manufacturing fluid dynamic muscles have not produced highly consistent results. Moreover, it is difficult using current techniques to install the elongated bladder within the braid when the braid is in an elongated state, and so it is difficult to achieve a maximum stroke for the muscle.